5. Localising Visual Field Defects Anatomically Flashcards
Where along the visual pathway and brain can a lesion be located to affect the visual field?
Pre-chiasmal -> ...
Brain
Chiasmal -> ..., ..., and ...
Post-chiasmal -> ..., ..., and ...
Where along the visual pathway and brain can a lesion be located to affect the visual field?
Pre-chiasmal -> optic nerve
Brain
Chiasmal -> chiasm, optic tract, and LGN
Post-chiasmal -> parietal lobe, occipital lobe, and other
What are the four descriptors needed to describe a visual field loss?
- Side -> R or L
- Nature -> Homonymous or bitemporal/binasal
- Congruity -> similarity is size and depth
- Type of defect -> hemianopia, sup/inf quadrantanopia, sup/inf sectoranopia, etc
Describe Optic Nerve defects.
They respect the ... and they show ....
The depth of the lesion produces near or distant effects:
* Deep lesions affect ..., result in ... of the ONH, and an ...
* Near lesions affect ..., result in ... of the ONH, and a ... if ...
Describe Optic Nerve defects.
They respect the horizontal raphe and they show arcuate patterns.
The depth of the lesion produces near or distant effects:
* Deep lesions affect the RGCs near the ON, result in cupping with a notch of the ONH, and an arcuate loss
* Near lesions affect the RGCs peripheral from the ON, result in saucerisation of the ONH, and a Bjerrum scotoma if nasal step/gap is present
What type of defects to chiasmal lesions result in?
Typically result in bitemporal VF defects. They might not be entirely bitemporal, but they RESPECT THE VERTICAL MIDLINE.
What is different about defects at or beyond the chiasm compared to pre-chiasmal defects?
They respect the vertical midline and they affect both eyes.
What type of defects do the following chiasmal lesions result in?
Anterior of optic chiasm - ... (small ..., ... and at the ...)
Lateral sides of optic chiasm - ... (hits ..., ... and ...) as ... is affected)
Posterior of optic chiasm - ... hemianopia
What type of defects do the following chiasmal lesions result in?
Anterior of optic chiasm - central hemianopic scotoma (small semicircle, temporally and at the centre)
Lateral sides of optic chiasm - junctional scotoma (hits both eyes, temporal and nasal) as Knee of von Hillebrand is affected)
Posterior of optic chiasm - bitemporal hemianopia
Explain bow tie/band optic atrophy and its effect on the visual field.
Prescence of lesion in ... involving crossed .... Typically, these defects are ... as the fibres from each eye are ....
Explain bow tie/band optic atrophy and its effect on the visual field.
Prescence of lesion in contralateral optic tract involving crossed retinal fibres nasal to the fovea. Typically, these defects are incongruent as the fibres from each eye are relatively separate within the optic tract.
Describe hemifield slide and how different phorias can affect it.
When total chiasmal lesion defects are present, the nasal portion of each eye’s visual field can result in a full visual field (with some small loss from the nose, perhaps).
No fusion results in manifestation of patient’s habitual heterophoria. In esophoria, there is a gap. In exophoria, there is overlap. In hyperphoria, there is vertical shift of one field.
Describe post-chiasmal lesions and how they affect the visual field.
Lesions to the temporal lobe result in homonymous ‘pie in the sky’ defects = superior quadrantanopia
Lesions to the parietal lobe result in homonymous ‘pie on the floor’ defects = inferior quadrantanopia
Lesions can be ‘foveal sparing’ in some people as they have dual blood supply to the cortex.
Describe cortical blindness in adults.
Definition: ...
Pupil reactions are ... and may have ....
E.g. ... Syndrome - px denies that they are blind because they have ... (... Syndrome)
Describe cortical blindness in adults.
Definition: total blindness due to bilateral occipital lobe lesions
Pupil reactions are okay and may have residual motion perception, blindsight.
E.g. Charles-Bonnet's Syndrome - px denies that they are blind because they have hallucinations (Anton's Syndrome)
